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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed March 2011

What is the official name of the SOS1 gene?

The official name of this gene is “SOS Ras/Rac guanine nucleotide exchange factor 1.”

SOS1 is the gene's official symbol. The SOS1 gene is also known by other names, listed below.

What is the normal function of the SOS1 gene?

The SOS1 gene provides instructions for making a protein that is involved in pathways within cells that control growth and development. This protein helps control (regulate) the activation of the RAS/MAPK signaling pathway, which helps control several important cell functions. Specifically, it regulates the growth and division of cells (proliferation), the process by which cells mature to carry out specific functions (differentiation), cell movement, and the self-destruction of cells (apoptosis). The SOS1 protein regulates another protein, called Ras, that stimulates cells to grow and divide. This regulation tightly controls the growth of cells and tissues, and is especially important for proper embryonic development.

Does the SOS1 gene share characteristics with other genes?

The SOS1 gene belongs to a family of genes called ARHGEF (Rho guanine nucleotide exchange factors).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? ( in the Handbook.

How are changes in the SOS1 gene related to health conditions?

Noonan syndrome - caused by mutations in the SOS1 gene

More than 20 mutations causing Noonan syndrome have been identified in the SOS1 gene. These mutations change single protein building blocks (amino acids) in the SOS1 protein. The resulting protein is continuously active, rather than switching on and off in response to other cellular proteins. This increase in protein activity disrupts the regulation of the RAS/MAPK signaling pathway that controls cell functions such as growth and division. This misregulation can result in the heart defects, growth problems, skeletal abnormalities, and other features of Noonan syndrome.

other disorders - caused by mutations in the SOS1 gene

Mutations in the SOS1 gene can also cause hereditary gingival fibromatosis type 1. This disorder is characterized by a slowly progressive overgrowth of the tissue of the gums (gingiva). Too much of this tissue can impair teeth from emerging through the gums, which can cause difficulties in speech and chewing food. At least one mutation in the SOS1 gene has been shown to cause hereditary gingival fibromatosis type 1. This mutation is an addition of a single building block of DNA (nucleotide). The mutation inserts the nucleotide cytosine into an area of the gene called exon 21 (written 3248_3249insC) and disrupts the gene's instructions, resulting a shortened protein. Unlike the normal SOS1 protein, the shortened protein is permanently active because it is missing areas that regulate its activity. Instead of triggering cell growth in response to particular signals from outside the cell, the overactive protein directs cells to grow and divide constantly. It is unclear why the overgrowth of tissue is seen only in the gums.

Where is the SOS1 gene located?

Cytogenetic Location: 2p21

Molecular Location on chromosome 2: base pairs 38,981,549 to 39,124,744

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The SOS1 gene is located on the short (p) arm of chromosome 2 at position 21.

The SOS1 gene is located on the short (p) arm of chromosome 2 at position 21.

More precisely, the SOS1 gene is located from base pair 38,981,549 to base pair 39,124,744 on chromosome 2.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about SOS1?

You and your healthcare professional may find the following resources about SOS1 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the SOS1 gene or gene products?

  • alternate SOS1
  • GF1
  • GGF1
  • gingival fibromatosis
  • gingival fibromatosis, hereditary, 1
  • HGF
  • son of sevenless homolog 1
  • son of sevenless homolog 1 (Drosophila)

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding SOS1?

acids ; apoptosis ; cell ; cytosine ; differentiation ; DNA ; embryonic ; exon ; gene ; gingiva ; gingival ; guanine ; gums ; hereditary ; mutation ; nucleotide ; proliferation ; protein ; RAS ; syndrome ; tissue

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Hart TC, Zhang Y, Gorry MC, Hart PS, Cooper M, Marazita ML, Marks JM, Cortelli JR, Pallos D. A mutation in the SOS1 gene causes hereditary gingival fibromatosis type 1. Am J Hum Genet. 2002 Apr;70(4):943-54. Epub 2002 Feb 26. (
  • Jang SI, Lee EJ, Hart PS, Ramaswami M, Pallos D, Hart TC. Germ line gain of function with SOS1 mutation in hereditary gingival fibromatosis. J Biol Chem. 2007 Jul 13;282(28):20245-55. Epub 2007 May 17. (
  • NCBI Gene (
  • Roberts AE, Araki T, Swanson KD, Montgomery KT, Schiripo TA, Joshi VA, Li L, Yassin Y, Tamburino AM, Neel BG, Kucherlapati RS. Germline gain-of-function mutations in SOS1 cause Noonan syndrome. Nat Genet. 2007 Jan;39(1):70-4. Epub 2006 Dec 3. (
  • Romano AA, Allanson JE, Dahlgren J, Gelb BD, Hall B, Pierpont ME, Roberts AE, Robinson W, Takemoto CM, Noonan JA. Noonan syndrome: clinical features, diagnosis, and management guidelines. Pediatrics. 2010 Oct;126(4):746-59. doi: 10.1542/peds.2009-3207. Epub 2010 Sep 27. Review. (
  • Shannon K, Bollag G. Sending out an SOS. Nat Genet. 2007 Jan;39(1):8-9. (
  • Tartaglia M, Pennacchio LA, Zhao C, Yadav KK, Fodale V, Sarkozy A, Pandit B, Oishi K, Martinelli S, Schackwitz W, Ustaszewska A, Martin J, Bristow J, Carta C, Lepri F, Neri C, Vasta I, Gibson K, Curry CJ, Siguero JP, Digilio MC, Zampino G, Dallapiccola B, Bar-Sagi D, Gelb BD. Gain-of-function SOS1 mutations cause a distinctive form of Noonan syndrome. Nat Genet. 2007 Jan;39(1):75-9. Epub 2006 Dec 13. Erratum in: Nat Genet. 2007 Feb;39(2):276. (
  • Zenker M, Horn D, Wieczorek D, Allanson J, Pauli S, van der Burgt I, Doerr HG, Gaspar H, Hofbeck M, Gillessen-Kaesbach G, Koch A, Meinecke P, Mundlos S, Nowka A, Rauch A, Reif S, von Schnakenburg C, Seidel H, Wehner LE, Zweier C, Bauhuber S, Matejas V, Kratz CP, Thomas C, Kutsche K. SOS1 is the second most common Noonan gene but plays no major role in cardio-facio-cutaneous syndrome. J Med Genet. 2007 Oct;44(10):651-6. Epub 2007 Jun 23. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: March 2011
Published: February 1, 2016